Pub: Spawning isolate it transformer not possible

[DartBot]

<img src="https://avatars.githubusercontent.com/u/648527?v=3" align="left" width="96" height="96"hspace="10"> Issue by Fox32
Originally opened as dart-lang/sdk#23105

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What steps will reproduce the problem?

1. Create an own pub transformer
2. Spawn a isolate using Isolate.spawn in Transformer.apply

What is the expected output? What do you see instead?

I would like to spawn a new isolate but instead I get the following exception:

in ShutdownIsolate: Unhandled exception:
Uncaught Error: IsolateSpawnException: Unhandled exception:
Uncaught Error: Load Error: FileSystemException: Cannot open file, path = 'C:\Users\Oliver\AppData\Local\Temp\pub_2d41cbb2-dc5b-11e4-bec2-90e6ba20879e\runInIsolate.dart' (OS Error: Das System kann den angegebenen Pfad nicht finden., errno = 3)
Stack Trace:

­0 _asyncLoadErrorCallback (dart:_builtin:268)

­1 _asyncLoadError (dart:_builtin:287)

­2 _loadDataAsyncLoadPort.<anonymous closure> (dart:_builtin:304)

­3 _RootZone.runUnary (dart:async/zone.dart:1155)

­4 _Future._propagateToListeners.handleValueCallback (dart:async/future_impl.dart:494)

­5 _Future._propagateToListeners (dart:async/future_impl.dart:577)

­6 _Future._complete (dart:async/future_impl.dart:358)

­7 _cancelAndValue (dart:async/stream_pipe.dart:62)

­8 Stream.first.<anonymous closure> (dart:async/stream.dart:911)

­9 _RootZone.runUnaryGuarded (dart:async/zone.dart:1093)

­10 _BufferingStreamSubscription._sendData (dart:async/stream_impl.dart:341)

­11 _BufferingStreamSubscription._add (dart:async/stream_impl.dart:270)

­12 _StreamController&&_SyncStreamControllerDispatch._sendData (dart:async/s

tream_controller.dart:698)

­13 _StreamController._add (dart:async/stream_controller.dart:570)

­14 _StreamController.add (dart:async/stream_controller.dart:516)

­15 _RawReceivePortImpl._handleMessage (dart:isolate-patch/isolate_patch.dart:142)

­0 _rootHandleUncaughtError.<anonymous closure> (dart:async/zone.dart:886)

­1 _asyncRunCallbackLoop (dart:async/schedule_microtask.dart:41)

­2 _asyncRunCallback (dart:async/schedule_microtask.dart:48)

­3 _runPendingImmediateCallback (dart:isolate-patch/isolate_patch.dart:96)

­4 _RawReceivePortImpl._handleMessage (dart:isolate-patch/isolate_patch.dart:143)

Stack Trace:

­0 Isolate._spawnFunction (dart:isolate-patch/isolate_patch.dart:347)

­1 Isolate.spawn (dart:isolate-patch/isolate_patch.dart:277)

­2 ImageTransformer.apply.<apply_async_body> (package:image_transformer/image_transformer.dart:76:15)

­3 _RootZone.runUnary (dart:async/zone.dart:1155)

­4 _Future._propagateToListeners.handleValueCallback (dart:async/future_impl.dart:494)

­5 _Future._propagateToListeners (dart:async/future_impl.dart:577)

­6 _Future._completeWithValue (dart:async/future_impl.dart:368)

­7 _Future._asyncComplete.<anonymous closure> (dart:async/future_impl.dart:422)

­8 _asyncRunCallbackLoop (dart:async/schedule_microtask.dart:41)

­9 _asyncRunCallback (dart:async/schedule_microtask.dart:48)

­10 _runPendingImmediateCallback (dart:isolate-patch/isolate_patch.dart:96)

­11 _RawReceivePortImpl._handleMessage (dart:isolate-patch/isolate_patch.dart:143)

­0 _rootHandleUncaughtError.<anonymous closure> (dart:async/zone.dart:886)

­1 _asyncRunCallbackLoop (dart:async/schedule_microtask.dart:41)

­2 _asyncRunCallback (dart:async/schedule_microtask.dart:48)

­3 _runPendingImmediateCallback (dart:isolate-patch/isolate_patch.dart:96)

­4 _RawReceivePortImpl._handleMessage (dart:isolate-patch/isolate_patch.dart:143)

What version of the product are you using?
Dart Editor version 1.10.0.dev_00_01 (DEV)
Dart SDK version 1.10.0-dev.0.1

On what operating system?
Windows 8.1 64bit

Please provide any additional information below.

Sometimes it would be useful to spawn an additional isolate to do multiple computation heavy operations in parallel. I think this problem is known and currently by design, but it the future it would be a nice addition.
Maybe it would work if pub wouldn't delete the runInIsolate.dart file in the temp folder intermediately, but on exiting pub?

[DartBot]

<img src="https://avatars.githubusercontent.com/u/5449880?v=3" align="left" width="48" height="48"hspace="10"> Comment by iposva-google

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Added Area-Pub, Triaged labels.

[DartBot]

<img src="https://avatars.githubusercontent.com/u/188?v=3" align="left" width="48" height="48"hspace="10"> Comment by nex3

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This is caused by a VM issue (issue dart-lang/sdk#6610) wherein existing script data isn't reused for Isolate.spawn. I don't think it's worth adding additional workarounds in pub rather than just solving the underlying problem.

It's worth noting that each transformer already runs in its own isolate, so it's unlikely that additional per-transformer parallelism is going to buy you a whole lot of value.

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Marked this as being blocked by dart-lang/sdk#6610.

[matanlurey]

We are no longer supporting transformers going forward, so a fix for this is not planned.